what filter do you recommend to use?
I heard using UV filter is good for protection but it will protect the lens from what? scratches?
There are plenty of threads that discuss this topic, so do a search to read all about the pros and cons of UV filters on lenses.
what do you think of using Circular Polarizing Filters and what is the best time to use it?
my main lens is 16-50 A77 kit.
I used MARUMI Circular Polarizing Filters but I don't really feel big different specially when I rotate it. there is any brand is recommend ?
If your polarizing filter is not doing much, check to be sure it is mounted the right way in the filter holder. I read a post from someone who had bought a filter that was mounted backwards. The easiest way to check it is to look through it at your computer monitor while you rotate the filter. The screen should black out when your eye is looking through the filter the same way your lens would be looking through it. If backwards, the screen will only show minor color shifts.
Also, the polarizer works best on the sky at about 90 deg to the direction of the sun.
my shooting always outdoor morning and evening.